As shown in FIG. 1, a conventional non-synchronous boost converter 10 generates output current by switching a power switch (not shown) in a controller chip 12, which flows through an inductor L1 and a Schottky diode D1 to charge a capacitor C2 to generate an output voltage VOUT. Since the forward voltage VF of the Schottky diode D1 is small, this converter circuit will have good efficiency in power conversion. However, when the boost converter 10 is shutdown by a signal Enable but the input voltage VIN provided by batteries is still high, for example at 3.7V, the Schottky diode D1 will be still conductive and thereby produce a non-zero output voltage, for example 3.3V, at the output voltage terminal VOUT. Therefore, leakage current will be present in this case and flow to the ground terminal GND through divider resistors R1 and R2, even the converter 10 has been shutdown. To avoid this leakage current, U.S. Pat. No. 7,126,314 to McGinty et al. replaces the general Schottky diode D1 with a gate-controlled Schottky diode and employs a LDMOS or JFET to provide a control signal to turn off the gate-controlled Schottky diode for load disconnection when the converter is shutdown. Another approach to avoid the leakage current is to insert a switch between the Schottky diode D1 and the output voltage terminal VOUT for load disconnection. However, the output VOUT of the boost converter 10 is a high voltage that typically ranges between 10V and 40V, and thus the switch must be a high-voltage device. Unfortunately, a high-voltage device not only is costly but also has a greater on-resistance, thereby causing poor efficiency in the converter circuit.
Therefore, it is desired a boost converter with a low-voltage device for load disconnection.